The present invention relates to digital printers and in particular ink jet printers.
Ink jet printers are a well known and widely used form of printed media production. Colorants, usually ink, are fed to an array of micro-processor controlled nozzles on a printhead. As the print head passes over the media, colorant is ejected from the array of nozzles to produce the printing on the media substrate.
Printer performance depends on factors such as operating cost, print quality, operating speed and ease of use. The mass, frequency and velocity of individual ink drops ejected from the nozzles will affect these performance parameters.
Recently, the array of nozzles has been formed using microelectromechanical systems (MEMS) technology, which have mechanical structures with sub-micron thicknesses. This allows the production of printheads that can rapidly eject ink droplets sized in the picolitre (xc3x9710xe2x88x9212liter) range.
While the microscopic structures of these printheads can provide high speeds and good print quality at relatively low costs, their size makes the nozzles extremely fragile and vulnerable to damage from the slightest contact with fingers, dust or the media substrate. This can make the printheads impractical for many applications where a certain level of robustness is necessary. Furthermore, a damaged nozzle may fail to eject the colorant being fed to it. As colorant builds up and beads on the exterior of the nozzle, the ejection of colorant from surrounding nozzles may be affected and/or the damaged nozzle will simply leak colorant onto the printed substrate. Both situations are detrimental to print quality.
To address this, an apertured guard may be fitted over the nozzles to shield them against damaging contact. Ink ejected from the nozzles passes through the apertures on to the paper or other substrate to be printed. However, to effectively protect the nozzles the apertures need to be as small as possible to maximize the restriction against the ingress of foreign matter while still allowing the passage of the ink droplets. Ideally, each nozzle would eject ink through its own individual aperture in the guard.
As the apertures in the guard are generally microscopic they can be easily clogged. Therefore, it is often desirable to keep the exterior of the nozzle guard clean especially in environments with relatively high levels of dust and other airborne particulates. This is conveniently achieved using a wiper blade that periodically sweeps across the exterior face of the guard to remove dust or ink residues. However, the residual matter on the wiper often becomes lodged on the exterior rim especially the portion of the rim facing into the wipers"" direction of travel. This build up of residue tends not to get removed by the wiper and can soon clog the aperture.
To overcome this, the exterior surface can have recesses around each of the apertures so that the wiper blade passes over without engaging the aperture rim. However, the recesses around each of the apertures require the spacing between adjacent apertures to increase. This in turn lowers the nozzle packing density on the printhead and thereby increases the printhead manufacturing costs.
Accordingly, the present invention provides an apertured nozzle guard for an ink jet printer printhead having an array of nozzles for ejecting colorant onto a substrate to be printed; wherein,
the nozzle guard is adapted to be positioned on the printhead such that it extends over the exterior of the nozzles to inhibit damaging contact with the nozzles while permitting colorant ejected from the nozzles to pass through the apertures and onto the substrate to be printed; the nozzle guard including:
an exterior surface that, when in use, faces the media;
the exterior surface being configured for engagement with a wiper blade that periodically sweeps the surface to remove residual matter; wherein,
the exterior surface has one or more recesses, each of the recesses encompassing a group of the apertures such that wiper blade is prevented engaging the exterior surface immediately adjacent any of the apertures in the group.
In this specification the term xe2x80x9cnozzlexe2x80x9d is to be understood as an element defining an opening and not the opening itself.
Preferably, the exterior surface further includes a deflector ridge in each of the recesses, the deflector ridge positioned to engage the wiper blade before the blade passes over any of the apertures within the group. In one convenient form, the deflector ridge is inclined to the direction of the wiper blade to deflect residual material away from the aperture and toward the edge of the recess. Similarly, the recesses may be generally rectangular wherein each side of the recess is inclined to the direction of the wiper blade during each sweep. A particularly preferred embodiment has an accumulation area partly defined by the last corner of the rectangular recess swept by the wiper blade.
The nozzle guard may further include fluid inlet openings for directing fluid over the nozzle array and out through the passages in order to inhibit the build up of foreign particles on the nozzle array.
The nozzle guard may include an integrally formed pair of spaced support elements one support element from the pair being arranged at each end of the guard.
In this embodiment, the fluid inlet openings may be arranged in one of the support elements.
It will be appreciated that, when air is directed through the openings, over the nozzle array and out through the passages, the build up of foreign particles on the nozzle array is inhibited.
The fluid inlet openings may be arranged in the support element remote from a bond pad of the nozzle array.
To optimize the effectiveness of the wiper blade, the exterior surface is flat except for the recesses and deflector ridges. By forming the guard from silicon, its coefficient of thermal expansion substantially matches that of the nozzle array. This will help to prevent the array of apertures in the guard from falling out of register with the nozzle array. Using silicon also allows the shield to be accurately micro-machined using MEMS techniques. Furthermore, silicon is very strong and substantially non-deformable.